When a gyratory crusher is in crushing operation, the crushing head, through the material being crushed, has rolling engagement with the concave and thus rotates, relative to the crusher frame and the eccentric, in the direction opposite to that of eccentric rotation. To accommodate such relative rotation of the crushing head it is freely rotatably mounted on the eccentric. However, in the absence of an anti-spin feature the crushing head tends to rotate in the same direction as the eccentric when the crusher is operating without a load. When material to be crushed is then fed between the freely spinning crushing head and the concave, the material retards the rotation of the head and in doing so detrimentally abrades the crushing elements and especially the concave.
U.S. Pat. No. 3,744,728, issued in 1973, disclosed a gyratory crusher wherein free spinning of the conical crushing head in the direction of rotation of the eccentric was prevented by means of a hydraulic motor connected between the crushing head and the eccentric. Under no-load conditions that motor drove the crushing head for rotation relative to the eccentric in the direction opposite to that of eccentric rotation and at a rotational speed equal to that of the eccentric. During crushing, friction between the concave and the crushing head imposed upon the crushing head a torque which supplemented that of the hydraulic motor, allowing the crushing head to rotate as necessary for its rolling engagement with the concave. This anti-spin mechanism was relatively expensive because of the cost of the hydraulic motor, which was of the gerotor type; and it was not consistently reliable in operation, owing to the difficulty of so controlling the feed of pressure oil to the hydraulic motor as to assure its being driven at exactly the rotational speed of the eccentric shaft.
A more recent anti-spin mechanism for gyratory crushers has comprised a one-way clutch connected between the crusher frame and the crushing head and arranged to confine the crushing head against rotation relative to the frame in the direction of eccentric rotation but to permit its substantially free rotation in the opposite direction. This arrangement had the advantage of being lower in cost than the hydraulic pump anti-spin mechanism, and it was satisfactorily operative under normal conditions.
However, it sometimes happens during a crushing operation that the crushing head is virtually locked to the eccentric and is compelled to rotate with it. This can occur when the crusher is somewhat overloaded and crushed material becomes jammed between the eccentric and the crushing head, or when very cold weather congeals the oil that lubricates the crushing head bearings. At such times the high torque transmitted to the crushing head from the eccentric shaft is imposed upon the one-way clutch, which cannot reasonably be designed to resist rotational forces of such magnitude.
To protect the one-way clutch from excessive torque in its rotation inhibiting direction, the connection between it and the crushing head has heretofore comprised a shear pin that was designed to break at a torque value safely below the maximum that the one-way clutch could support. With some materials put through the crusher, breaking of the shear pin was an almost daily occurrence. Each such breakage required shut-down of the crusher and replacement of the broken pin. Since the crusher was out of service for at least half an hour during this operation, the shearing of a pin was very expensive in terms of lost production.
It is perhaps obvious that a torque limiting shear pin can be replaced by a clutch-like torque limiting device under some circumstances. But torque limiters heretofore available have not been suitable for gyratory crushers. The great majority of torque limiters release at torque values well below those normal in gyratory crusher operation and therefore cannot be used in an anti-spin mechanism. Many torque limiters, once released, must be reset either by effecting reverse relative rotation of the parts connected by the device or by performing a resetting operation on the device with the use of a special tool; and in either case resetting of such a torque limiter, if it were installed in a crusher, would necessitate shut-down of the crusher for some period of time.
Owing to the eccentric arrangement of a seal which normally surrounds the crushing head and protects the bearings that rotatably support it on the eccentric shaft, a jam that tends to lock the crushing head to the eccentric shaft usually clears itself in one revolution of that shaft. For this reason the most desirable type of torque limiter for the purpose here under consideration is a so-called automatic random reset device, which simply resets itself to its torque transmitting condition as soon as a torque overload is relieved, irrespective of the then-existing relative positions of rotation of the parts connected by the device. Although some automatic random reset torque limiters have heretofore been available, they have not been suitable for gyratory crusher anti-spin applications. Among other objections is the fact that known devices of this type have not been so configured that they could be installed as direct replacements for the heretofore conventional shear pin assembly, so that adapting the crusher for such a device would have necessitated a substantial and expensive redesign of the crushing head and possibly also of the eccentric shaft.